Abstract:

A light output device comprises a substrate arrangement comprising a
plurality of light source circuits integrated into the structure of the
substrate arrangement. Each light source circuit comprises a light source
device arrangement (4) having two terminals and a transistor circuit (7).
Each light source circuit is supplied with power from an associated pair
the power connections (10,11,14,15,20), and at least two light source
circuits (4,7) share the same pair of power connections. A set of control
connections (18) are provided for receiving external control signals for
controlling the transistor circuits (7). A set of non-overlapping
electrodes (10,11,14,15,18,20) provide the internal connections between
the power connections, the light source device terminals and the
transistor circuits, and each light source device is individually
independently controllable.

Claims:

1. A light output device comprising:a substrate arrangement;a plurality of
light source circuits integrated into the substrate arrangement, each
light source circuit comprising a light source device arrangement having
two terminals and a transistor circuit;a set of power connections for
receiving external power, wherein each light source circuit is associated
with a pair of the power connections for the supply of power to the light
source circuit, and wherein at least two light source circuits share the
same pair of power connections;a set of control connections for receiving
control signals for controlling the respective transistor circuits; anda
set of non-overlapping electrodes for providing internal connections
between the power connections, the light source device terminals and the
transistor circuits,wherein each light source device arrangement is
individually and independently controllable.

2. A device as claimed in claim 1, each light source device arrangement
comprises a single light source device.

3. A device as claimed in claim 1, wherein each transistor circuit
comprises a single transistor.

4. A device as claimed in claim 3, wherein each transistor comprises a
MOSFET.

5. A device as claimed in claim 1, wherein each transistor has its gate
connected to a respective control connection.

6. (canceled)

7. A device as claimed in claim 5, wherein the at least two light source
circuits which share the same pair of power connections are connected in
series between the power connections, with each transistor connected in
parallel across the light source device arrangement.

8. A device as claimed in claim 7, further comprising a power source
arrangement, comprising a current source for each set of light source
circuits which share the same pair of power connections.

9. A device as claimed in claim 7, further comprising a control circuit
for controlling the transistor circuits, wherein the control levels
applied to the transistors are selected in dependence on which light
source circuits are turned on and which are turned off.

10. A device as claimed in claim 1, comprising a control circuit for
dimming the light intensity of a light source device using duty cycle
control.

11. A device as claimed in claim 1, wherein one of the power connections
is shared between all light source circuits.

12. A device as claimed in claim 1, wherein the electrodes comprise at
least semi-transparent conductors.

13. A device as claimed in claim 1, wherein the light source device
comprises an LED device or a group of LED devices.

14. A device as claimed in claim 13, wherein the light source device
comprises an inorganic LED, an organic LED, a polymer LED or a laser
diode.

15. (canceled)

16. A lighting system comprising a light output device as claimed in claim
1 and a lighting controller, wherein the substrate arrangement comprises
first and second transparent substrates and an electrode arrangement
embedded in the substrate arrangement, with the plurality of light source
circuits connected to the electrode arrangement.

17. A lighting system as claimed in claim 16, wherein a thermoplastic or
resin layer is provided between the substrates.

18. A lighting system as claimed in claim 16, wherein the electrode
arrangement is formed of a transparent conductive material.

19. A lighting system as claimed in claim 18, wherein the electrode
arrangement is formed of a transparent metal oxide.

20. A lighting system as claimed in claim 16, wherein the transistors of
the transistor circuits comprise a transparent transistor in a
transparent package.

Description:

[0002]One known example of this type of lighting device is a so-called
"LED in glass" device. An example is shown in FIG. 1. Typically a glass
plate is used, with a transparent conductive coating (for example ITO)
forming electrodes. The conductive coating is patterned in order to make
the electrodes, that are connected to a semiconductor LED device. The
assembly is completed by laminating the glass, with the LEDs inside a
thermoplastic layer (for example polyvinyl butyral, PVB).

[0003]Applications of this type of device are shelves, showcases, facades,
office partitions, wall cladding, and decorative lighting. The lighting
device can be used for illumination of other objects, for display of an
image, or simply for decorative purposes.

[0004]One problem with this type of device is that it is difficult to
provide a structure which enables individual LEDs in the glass to be
turned on and off, for example in order to display an image, or a dynamic
pattern. This is difficult, because a two-dimensional pattern of
transparent electrodes is desired, but crossovers need to be avoided if
the layer structure is to be kept simple. if individual wires are used
for each LED (instead of a two dimensional pattern), this results in very
high wire resistances (for example ITO electrodes), leading to high
electrical losses in these wires.

[0005]It is an object of the invention to provide independent control of
the light source devices but with a simple conductor pattern.

SUMMARY OF THE INVENTION

[0006]According to the invention, there is provided a light output device
comprising:

[0007]a substrate arrangement;

[0008]a plurality of light source circuits integrated into the structure
of the substrate arrangement, each light source circuit comprising a
light source device arrangement having two terminals and a transistor
circuit;

[0009]a set of power connections for receiving external power, wherein
each light source circuit is associated with a pair of the power
connections for the supply of power to the light source circuit, and
wherein at least two light source circuits share the same pair of power
connections;

[0010]a set of control connections for receiving control signals for
controlling the respective transistor circuits; and

[0011]a set of non-overlapping electrodes which provide the internal
connections between the power connections, the light source device
terminals and the transistor circuits,

[0013]This arrangement provides individually addressable light source
circuits, using non-overlapping electrodes so that a single electrode
layer can be used, but which reduces the number of power connections to
the plurality of light source circuits. This enables the width of the
power connections to be increased for a given pitch between light source
circuits, or enables the pitch to be reduced. Transistor circuits enable
the independent control to be achieved despite the shared power
connections.

[0014]Each light source device arrangement can comprise a single light
source device and each transistor circuit can comprise a single
transistor. This provides a simple architecture.

[0015]Each transistor can comprise a MOSFET with its gate connected to a
respective control connection.

[0016]In one example, each transistor can have its source and drain
connected to respective power connections, with one of the source and
drain connected to a power connection through the transistor. If these
are side by side, the power connections can be shared and doubled in
width, and narrow control lines can be used to control the transistors
(because of the low current requirement).

[0017]In another example, the at least two light source circuits which
share the same pair of power connections can be connected in series
between the power connections, with each transistor connected in parallel
across the light source device arrangement. In this arrangement, a
current path is set through a chain of light source device arrangements,
and the parallel transistors enable the controlled light source device
arrangement to be bypassed.

[0018]Preferably in this case, a power source arrangement comprises a
current source for each set of light source circuits which share the same
pair of power connections. In this way, no matter how many light source
device arrangements are connected in series, they can all be illuminated.
A control circuit can then be provided for controlling the transistor
circuits, with the control levels applied to the transistors being
selected in dependence on which light source circuits are turned on and
which are turned off. This can be required as the voltage levels are not
static.

[0019]In all examples, a control circuit can be provided for dimming the
light intensity of a light source device using duty cycle control.

[0020]Preferably, one of the power connections is shared between all light
source circuits.

[0021]The light source device arrangements can comprise an LED device or a
group of LED devices, for example inorganic LEDs, organic LEDs, polymer
LEDs or a laser diodes.

[0022]The invention also provides a lighting system comprising a light
output device of the invention, and a lighting controller for controlling
the signals provided to the control circuits.

[0023]It is noted that the invention relates to all possible combinations
of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]Examples of the invention will now be described in detail with
reference to the accompanying drawings, in which:

[0025]FIG. 1 shows a known LED in glass illumination device;

[0026]FIG. 2 shows a single LED of the device of FIG. 1 in more detail;

[0027]FIG. 3 shows one way to provide independent control of multiple
light source devices;

[0028]FIG. 4 shows a first example of light output device of the
invention; and

[0029]FIG. 5 shows a second example of light output device of the
invention.

[0030]The same reference numbers are used to denote similar parts in the
different figures.

DETAILED DESCRIPTION

[0031]The structure of an LED in glass illumination device is shown in
FIG. 2. The lighting device comprises glass plates 1 and 2. Between the
glass plates are (semi-) transparent electrodes 3a and 3b (for example
formed using ITO), and a LED 4 connected to the transparent electrodes 3a
and 3b. A layer of thermoplastic material 5 is provided between glass
plates 1 and 2 (for example PVB or UV resin).

[0032]The glass plates typically may have a thickness of 1.1 mm-2.1 mm.
The spacing between the electrodes connecting to the LED is typically
0.01-3 mm, for example around 0.15 mm. The thermoplastic layer has a
typical thickness of 0.3 mm-2 mm, and the electrical resistance of the
electrodes is in the range 2-80 Ohm, or 10-30 Ohms/square.

[0033]The electrodes are preferably substantially transparent, so that
they are imperceptible to a viewer in normal use of the device. If the
conductor arrangement does not introduce a variation in light
transmission (for example because it is not patterned, or because the
pattern cannot be seen), a transparency of greater than or equal to 50%
may be sufficient for the system to be transparent. More preferably, the
transparency is greater than 70%, more preferably 90%, and even more
preferably 99%. If the conductor arrangement is patterned (for example
because thin wires are used), the transparency is preferably greater than
80%, more preferably 90%, but most preferably greater than 99%.

[0034]The electrodes can be made of a transparent material such as ITO or
they can be made of an opaque material such as copper but be sufficiently
thin so that they are not visible in normal use. Examples of suitable
materials are disclosed in U.S. Pat. No. 5,218,351.

[0035]FIG. 3 shows an example of an electrode pattern for controlling
individual LEDs. Individual wires 10-15 are used to control several
respective LEDs 4. The wires are made using a laser to make cuts 6 in a
layer of electrode material 3. A problem with this solution is that the
wires 10-15 are very thin, which results in a very high resistance, and
accordingly in a high loss of electric power.

[0036]The current invention provides an alternative solution for
controlling multiple light sources (such as LEDs) embedded in a substrate
(such as glass). The control of individual light sources enables display
of an image, or other dynamic pattern.

[0037]The invention provides an arrangement in which light source circuits
are provided (comprising at least a light source and a control
transistor) and these are supplied with power from an associated pair of
power connections. At least two light source circuits share the same pair
of power connections so that the number of power connections is reduced
and their dimensions can be increased.

[0038]FIG. 4 shows a first embodiment according to the present invention.
In this arrangement, each light source 4 has a transistor 7, with the
gate of the transistor connected to a control wire 18. The transistor and
light source together form a light source circuit.

[0039]Each light source 4 is in series between a high power rail electrode
10,11,14,15 and a shared low power rail electrode 20. Each high power
rail electrode 10,11,14,15 is shared between two light sources 4, so that
two adjacent light sources share the same pair of power electrodes. They
can thus be made wider.

[0040]In this arrangement, for a number n of light sources, there are
(n/2+1) power electrodes. As shown, these electrodes are defined by areas
of conductor over the substrate, separated by score lines. These
electrode areas define the internal (i.e. on-substrate) connections
between the light sources, the transistors and the power and control
lines. All the electrodes are defined by a single layer and are
non-overlapping, and power or control signals are applied at the
periphery.

[0041]The transistor 7 associated with each light source enables the light
source to be isolated from one of the power conductors. In the example
shown, one light source of a pair can be isolated from the high power
rail and the other can be isolated from the low power rail, but this does
not need to be the case. Instead, the transistors can all be associated
with the high or low power rails.

[0042]The control gate of each transistor is connected to a control wire
18. By applying a voltage to control wire 18, the transistor can be
switched on and off, which subsequently will turn the corresponding light
source 4 on or off.

[0043]Compared to FIG. 3, the number of electrode wires has been reduced
by approximately a factor of 2 (from n+1 to n/2+1), because the
electrodes 11 and 12 in FIG. 3 have been merged into 11 in FIG. 4, and
electrodes 13 and 14 in FIG. 3 have been merged into electrode 14.

[0044]It is also possible to reduce the number of electrodes by more than
a factor of two. This is achieved by powering more light sources using
the same pair of power lines, as shown in FIG. 5.

[0045]In the example shown, three light source circuits 4,7 share the same
pair of power connections (although none of the three light source
circuits is directly connected to both power connections). These sets of
light source circuits are in columns in FIG. 5, with the high power rail
at the top and the low power rail at the bottom. The light sources are
connected in series between the power connections, with each transistor 7
connected in parallel across the light source 4. It will be understood
that "sharing" power connections means that the same power connections
are used directly or indirectly to supply power to the light source
circuit.

[0046]Thus, in each column in FIG. 5, there are three control lines 18,
one for each light source circuit in the column. Electrode areas (at
intermediate voltages in use) are provided between the light sources as
well as defining the power connections.

[0047]In this arrangement, a current path is set through a chain of light
sources 4, and the parallel transistors 7 enable the controlled light
source device arrangement to be bypassed. Thus, the transistors 7 are
used as dynamic shunts. This means that the transistor is connected in
parallel to the LIGHT SOURCE. If the transistor is turned on, the current
will flow through the transistor and the light source stays off. The
transistors used are preferably MosFETs.

[0048]In this arrangement, a current flow is maintained between the power
lines independently of the on/off state of the light sources, and this
enables multiple light sources to be chained together, unlike in the
version of FIG. 4.

[0049]In all examples, the transistors can be controlled to turn the
associated light sources periodically on and off. This may be used for
dimming the light source intensity using duty cycle control. For example,
by turning the light source on and off with a 50% duty cycle, the light
output intensity will be reduced to 50%. Preferably, this is implemented
at a high frequency, such that the human eye cannot observe the intensity
modulation.

[0050]In the example of FIG. 5, the reference levels required for
switching the transistors depend on the number of light sources emitting
light in the column, between the main reference level and the reference
level of the transistor. This is because the voltage levels will depend
on which light sources are turned on and which transistors are turned on.

[0051]The switching commands determining the timing and duty cycle control
for the light sources can be generated by a digital circuit referenced to
the main power line reference levels. Level shifters can then be used
between the digital circuit and the transistors so that the digital
control signals output by the digital circuit are converted into
appropriate voltage levels for application to the transistor gates.

[0052]Each string of light sources in the example of FIG. 5 is preferably
driven by a current source, again because the required voltage levels
depend on the light sources which are turned on. A switched mode current
source can be used.

[0053]In a preferred embodiment, the transistors 7 are invisible to the
naked eye. This can be achieved by embedding transparent transistors, in
a transparent package. Transparent transistors are known and there are
existing transistor designs suitable for this application. The use of
very small transistors, which are barely visible is another option.

[0054]The examples above have shown a small array of light sources.
However, it will be understood that the invention is typically
implemented as many LED devices, embedded in a large glass plate. A
typical distance between the LEDs may be 1 cm to 10 cm, for example
approximately 3 cm.

[0055]Each light source may also comprise a single LED or multiple LEDs.

[0056]The examples above use glass substrates, but it will be apparent
that plastic substrates may also be used.

[0057]The LED array and the required control circuit may be merged into
one integrated device, or they may be connected with a low-resistance
interconnect.

[0058]In the detailed examples above, the number of electrodes is reduced
by having one common electrode between the light source circuits (low
power rail 20). Of course, the electrode 20 may also be split in parts,
such that each high power rail electrode corresponds with one low power
rail electrode. This may make driving electronics simpler.

[0059]Various modifications will be apparent to those skilled in the art.